Method for bleaching fibrous materials and compositions therefor

ABSTRACT

A bleaching composition for a fibrous material comprises an aqueous medium having dissolved therein sodium chlorite and sodium polyphosphate, said sodium polyphosphate being such that the molar ratio of Na2O to P2O5 is greater than 0.1 but less than 1.0 and that a 1 weight percent aqueous solution thereof has a pH of not higher than 3; and a method for bleaching a fibrous material comprises bleaching a fibrous material with said composition.

EJite States atent [191 Hkeda 221 Filed: Dec. 10, 1971 21 Appl. No.: 206,874

[52] U.S. Cl ..'8/108, 252/99, 252/187, 252/135, 423/304, 423/305, 423/315 [51] Int. Cl D06! 3/08 [58] Field of Search 8/108; 252/99, 187, 135; 423/304, 305, 315

[56] References Cited UNITED STATES PATENTS 3,111,358 11/1963 Doerr 8/108 2,367,771

1/1945 Hampel 8/108 Feb.5,1974

3,378,341 4/1968 Hartlapp et a1 423/315 3,547,573 12/ 1 970 2,900,219 8/1959 3,063,782 11/1962 3,173,749 3/1965 Hintzmann et a1. 8/108 Primary Examiner-Mayer Weinblatt Attorney, Agent, or Firm-Toren and McGeady 57 ABSTRACT 3 Claims, No Drawings 1 METHOD FOR BLEACHING FIBROUS MATERIALS AND (IOMPOSHTTONS THEREFOR This invention relates to a method for bleaching fibrous materials and compositions therefor, more particularly to improvements in a method and composition for bleaching fibrous material using sodium chlorite as a bleaching component.

Sodium chlorite is widely used for bleaching fibrous materials made of cellulosic fibers, such as, cotton, hemp, rayon, etc. and synthetic fibers, such as, nylon, polyester, polyacrylonitrile, etc. For bleaching with sodium chlorite, an organic acid, such as, oxalic acid, formic acid, acetic acid, sulfamic acid acid or an inorganic acid, such as, sulfuric acid has been used as an activating agent for decomposing sodium chlorite to generate chlorine dioxide gas. However, when such known activating agent is used, generation of the chlorine dioxide gas cannot be controlled as desired but an excess amount of the gas will inevitably result. This gives rise, not only, to waste of the chlorine source, but also, causes corrosion of the apparatus and deterioration in the fibrous materials. Further, oxalic acid and sulfamic acid per se corrode metal and, therefore, when such acids are used, metal containers undergo marked corrosion. For these reasons, it has heretofore been necessary to add a gas controlling agent and/or an anticorrosive agent to the bath. But even the use of such chemical agents has not achieved satisfactory results. Moreover, use of these organic acids elevates the BOD (biochemical oxygen demand) of the waste liquid from bleaching treatment and requires troublesome aftertreatment.

Accordingly, an object of this invention is to provide a novel activating agent for sodium chlorite which in itself is low in metal-corroding properties and is capable of effectively decomposing sodium chlorite without generating an excess of chlorine dioxide gas that will cause corrosion and without noticeably elevating the BOD of the liquid.

Another object of this invention is to provide a composition capable of bleaching fibrous materials made of v cellulosic fibers and various synthetic fibers to a high degree without causing corrosion to the apparatus and deterioration in the fibrous materials.

Another object of this invention is to provide a method for bleaching fibrous materials whereby such fibrous materials can be bleached effectively without any deterioration in their properties.

These objects ot this invention will become more apparent from the description to follow.

The bleaching composition of this invention comprises an aqueous medium having dissolved therein sodium chlorite and sodium polyphosphate in an amount of 0.8 to 3.5 times the weight of C10 contained in the sodium chlorite, the sodium polyphosphate being such that a molar ratio of Na O to P (this molar ratio being hereinafter referred to as R") is greater than 0.1

but less than 1.0 and that 1 wt percent aqueous solution thereof has a pH of not higher than 3.

The present inventors researches have shown that a specific sodium polyphosphate, when used as an activating agent for sodium chlorite, decomposes sodium chlorite to continuously generate a suitable amount of C in conformity with the need for bleaching, without causing corrosion to the apparatus and deterioration in the fibrous materials due to the generation of 2 excess ClO but ensuring efficient bleaching of the fibrous materials.

The sodium polyphosphate to be used in accordance with this invention must be such that the molar ratio, R, is greater than 0.1 but less than 1.0 and that a 1 wt percent aqueous solution thereof has a pH of not higher than 3. It is only such sodium polyphosphate of the foregoing characteristics that assures outstanding effects when acting as an activating agent for sodium chlorite. Such sodium polyphosphate will hereinafter be referred to as sodium ultraphosphate. In the case of the other usual polyphosphates, such as, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate and the like in which R is equal to or larger than 1, these are essentially different in properties from sodium ultraphosphate in which 0. l R l .0. In fact, unlike the latter, the pH of a 1 wt percent aqueous solution of the former is 7 to 9 and they do not display an activating effect on sodium chlorite at all.

The sodium ultraphosphate to be used in accordance with this invention may preferably be such that 0.3 all 9-8- Th so la a tta ao n tat t9, e u d in accordance with this invention is known and is readily available and easy to manufacture. For example, sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium phosphate is mixed with phosphoric acid or phosphorus pentoxide in such an amount that 0. l R l .0, and the mixture is melted at about 650 C for reaction, whereby the desired sodium ultraphosphate will be obtained.

The bleaching composition of this invention is prepared by dissolving sodium chlorite and sodium ultraphosphate in water. The concentration of sodium chlorite usually is 1 to 3 g/liter, preferably 2.0 to 2.7 g/liter. Sodium ultraphosphate is used in an amount of 0.8 to 3.5 times the weight of C10 contained in the sodium chlorite. If the sodium ultraphosphate is used in an amount of less than the above amount, it will not effectively act on sodium chlorite, although an amount of more than the above will cause damage to fibrous materials. It is preferable to use sodium ultraphosphate in an amount of 1.0 to 3.0 times the weight of C10 contained in the sodium chlorite. If the pH of the bleaching composition of this invention is very low, the fibrous materials to be treated may be deteriorated, so that it is desired that the composition have a pH of 2.5 to 5.0.

To improve the hand of the fibrous materials treated and more efficiently preclude any possible deterioration in the fibrous materials, at least one compound from the group of urea, hydrazine and ammonium phosphate may be added alone or in admixture with one another to the composition. lt is desired that such additives be used in an amount of 20 to 50 wt percent, based on the .weight of the sodium chlorite. If the amount exceeds 50 wt percent, the stability of the bath will be impaired which is undesirable. The composition may further contain various known additives, such as,

a surface active agent to assure improved penetration I of effective ingredients into the fibrous materials to be treated, or fluorescent dye to add to the whiteness of the fibrous materials.

The present composition can be used for bleaching various fibrous material such as fibers, yarns, woven fabrics, knitted fabrics, nonwoven fabrics, etc., capable of being bleached with sodium chlorite. For instance, it can be applied to fibrous materials made of cellulosic fibers such as cotton, hemp, rayon, etc., and made of various synthetic fibers such as nylon, polyester, polyacrylonitrile. etc. Bleaching is conducted under the same conditions as heretofore employed for sodium chlorite. With this invention. bleaching can be effected even within a shorter period of time under milder conditions. More specifically, the fibrous materials to be bleached is placed into a bath of room temperature and the bath is then heated to about 80 to 98 C to effect bleaching of the fibrous materials-The ratio in weight of the fibers to the bath may suitably be 1 5 to l 50. The heating time may vary in accordance with the kinds of fibrous materials to be treated. For fibrous materials made of acrylic fibers, for example, good results will usually be achieved by heating for about 20 to 30 minutes, and for cotton, for about.30 to 60 minutes. This is about half the time required for bleaching with sodium chlorite conducted in usual manner. The bleached fibrous materials are then dechlorinated as by treating with an aqueous solution of acid sodium sulfite in conventional manner and washed with water and dried.

For a better understanding of the invention examples are given below.

EXAMPLE i S odium chlorite containing 25 wt percent 1.5 g/liter of available chlorine:

Water: Amount necessary for making one liter bath 25 g of polyacrylonitrile cloth was placed in the abovementioned bath at 30 C. Thereafter the bath was heated to 97 C in minutes and kept at that temperature for 30 minutes. After the bath was cooled to room temperature the cloth was taken out from the bath and then placed in the aqueous solution of acid sodium sulfite dissolved in a concentration of l g/liter. The solution was then heated at 60 to 70 C for 10 minutes for dechlorination of the cloth. The cloth was then washed with water and dried to obtain bleached cloth.

COMPARISON EXAMPLE 1 For comparison, polyacrylonitrile cloth was bleached in the same manner as in Example 1, except that the bath having a following compositions was used.

Sodium chlorite containing 25 1.5 g/liter wt percent of available making one liter bath Tests were performed on the cloth obtained in Example l and Comparison l with the results shown in Table 1 below. in which whiteness and colour fasteness to light were measured by the following methods.

whiteness: Hunter's method disclosed in HS L l073 Using Fade-Ometer in accordance with Colour fastness to light:

Tensile strength Test was conducted on each cloth under standard conditions using Schoppers fiber tensile tester. The results are shown in Table 2.

TABLE 2 Tensile strength (g/Z cm) Strength Lengthwise Crosswisc Total lowering rate (F) (W+F) '7, i

Original cloth 1400 i050 2450 0 Bleached cloth of Example 1 H30 1 I00 2230 9.0

Bleached cloth of h comparison 1 I260 930 2190 11.0

Corrosive property of the bath used was tested using stainless steel test piece (SUS 27, 30 mm x 50 mm x 2 mm). The test piece was immersed in each-bath of Example 1 and Comparison 1 and heated under the same conditions as in Example 1. The test piece thus treated was then washed with water and with 15 wt percent hydrochloric acid containing 1 wt percent of lbit IL 100 (trade mark, Sumitomo Kagaku Kabushiki Kaisha, Japan). Further the piece was washed with water and with methanol, followed by drying to determine corrosive loss. The result is shown in Table 3 below.

TABLE 3 Corrosive loss Bath of 010068 mg (740 mg/l O cm /dayl Example 1:

Bath of 0.131 mg (1420 mg/lO cmlday) Comparison 1:

EXAMPLE 2 Sodium chlorite containing 25 wt percent of 2.67 g/liter available chlorine:

Sodium ultraphosphate:

"Micawhite ATN cone. (trade mark. the same as in Example 1 Water:

0.67 g/liter 5 0.34 g/liter Amount necessary for making one liter bath 30 g of polyacrylonitrile cloth was placed in the abovementioned bath at 30 C and bleached in the same manner as in Example 1, whereby bleached cloth was obtained.

COMPARISON EXAMPLE 2 Except that the following bath was used, polyacrylonitrile cloth was treated in the same manner as in Example 2.

Water:

Sodium chlorite containing 25 wt percent of 2.67 g/liter available chlorine:

Acetic acid: 1.24 g/liter Micawhite ATN cones" (trade mark. the 0.34 g/liter same as in Example 1):

Sodium nitrite: 0.67 g/liter Amount necessary for making one liter bath The properties of the bleached cloth obtained in Example 2 and Comparison 2 are shown below.

The properties were measured by the following methods.

Whitcness (percent):

Discoloration Urea: 0.34 g/liter lMicawhite ATNconc.")trade mark, 0.34 g/liter the same as in Example 1): Water: Amount necessary for making one liter bath 25 g of polyacrylomtrile cloth was placed in the abovementioned bath and heated to 90 C in 25 minutes. The bath was kept at that temperature for minutes and the cloth thus bleached was subjected to dechl o rination washing and drying in the same manner as in Example 1.

COMPARISON EXAMPLE 3 Except for using the bath having the following compositions the polyacrylonitrile cloth was treated in the same manner as in Example 3 to obtain bleached cloth.

Sodium chlorite containing 90.45 percent of l g/liter available chlorine:

Oxalic acid: I g/liter Nonionic surfactant: 0.34 g/liter Micawhite ATN conc." (trade mark, the 0.34 g/liter same as in Example 1):

Water: Amount necessary for making one liter bath The properties of the cloth obtained by the method of Example 3 and Comparison 3 are shown in the following Table 5. Tearing strength were measuredip accordance with the method disclosed in J [S L l00 4 and other tests were performed in the same manner as described before TABLE 5 Property Example 3 Comparison 3 whiteness (percent) 82.0 82.5

Tearing strength: Lcngthwise (720 g) Lengthwise (670 g) crosswise (670 g) Crosswise (670 g) Touch to hand +l -ll- Discoloration to heat No change was No change was processing: observed observed What we claimis:

1. A method for bleaching a fibrous material which tissst etins the ma w sble s n wmposition gonsisting essentially of an aqueous medium having dissolved therein sodium chlorite and sodium polyphosphate in an amount of 08 to 3.5 times the weight of the Cl 0 contained in the sodium chlorite, said sodium polyphosphate being such that the molar ratio of Na O to P 0 is greater than 0.1 but less than 1.0 and that a 1 weight percent aqueous solution thereof has a pH of not higher than 3, said treatment being carried out at a temperature from about to 98 C and for a time period from about 20 to 60 minutes, and then washing the treated material.

2. The bleaching method according to claim 1, in which said molar ratio of the sodium polyphosphate is in the range of 0.3 to 0.8.

3. The bleaching method according to claim 1, in which said sodium polyphosphate is present in an amount of 1.0 to 3.0 times the weight of the C10 contained in the sodium chlorite. 

2. The bleaching method according to claim 1, in which said molar ratio of the sodium polyphosphate is in the range of 0.3 to 0.8.
 3. The bleaching method according to claim 1, in which said sodium polyphosphate is present in an amount of 1.0 to 3.0 times the weight of the ClO contained in the sodium chlorite. 